FIG. 1 is a schematic diagram showing a stereoscopic image implementation method using a general projector, a modulator and 3D glasses.
An image generated by the projector 1 is converted into linearly polarized light to be transmitted through the modulator 2. By driving the modulator 2 using a signal linked with the projector 1, image light transmitted through the modulator 2 is modulated into circularly polarized light in a clockwise or counterclockwise direction and is radiated onto a screen. Image light reflected from the screen may be presented to a viewer as a stereoscopic image through the 3D glasses 4.
FIG. 2 is a diagram showing the configuration of a conventional modulator.
Linearly polarized incident light is emitted by sequentially passing through a transparent substrate 9, a transparent electrode 8, a liquid crystal (LC) layer 7, a transparent electrode 6 and a transparent electrode 5.
The transparent electrodes 6 and 8, which are spaced apart from each other, are driven by a voltage drive device 10 using different voltages, such that the emitted light is converted into circularly polarized light in a clockwise or counterclockwise direction.
FIG. 3 is a diagram showing a light traveling path in an LC layer according to an angle of incidence of incident light.
If the angle of incidence is not perpendicular to the LC layer 13 and is θ1, a difference between the thickness d of the LC layer 13 and the length l of the beam of light transmitted through the LC layer 13, that is, (l−d), is as follows.l−d=d(1/Cos [A Sin {(n1/n2)Sin θ1}]−1)  Equation 1
where, n1 denotes a refractive index of air and is 1 and n2 denotes a refractive index of the LC layer and is about 1.5.
FIG. 4 is a diagram showing an optical path difference (l−d)/d according to change in angle of incidence θ1 based on Equation 1.
In FIG. 4, an optical path difference of 0% corresponds to the case where light is perpendicularly incident on the LC layer. When the angle of incidence increases, l becomes greater than d and thus the optical path difference increases.
A maximum angle of incidence is determined by a throw ratio (TR; distance between the projector and the screen/width of the screen) of the stereoscopic image system. For example, the maximum angle of incidences when the TR is 1.5 and 1.3 are about 18 degrees and 21 degrees, respectively.
Accordingly, the optical path differences are 2.1% (in the case of 18 degrees) and 3.0% (in the case of 21 degrees). Since polarization conversion efficiency is proportional to the optical path difference, phase retardation occurs. Circularly polarized light conversion efficiencies of light passing through the center part and outermost part of the modulator are respectively 2.1% and 3.0% due to the optical path difference.
TR is 1.3 and a value obtained by averaging the optical path differences when the angle of incidence is 1 to 24 degrees is 1.4%.
By this difference, crosstalk occurs in images perceived by the left and right eyes through the 3D glasses 4, such that the image quality of the stereoscopic image deteriorates.
As described above, in addition to the problem of the modulator for the stereoscopic image device, the stereoscopic image device using the beam splitter for high-luminance stereoscopic image implementation has the following problems.
FIG. 5 is a side view of a beam splitter used in a stereoscopic image device for high-luminance stereoscopic image implementation.
As shown in FIG. 5, in the beam splitter used in the stereoscopic image device, when light having a mixture of P-polarized light and S-polarized light is input to the beam splitter 1, the P-polarized light may be transmitted and the S-polarized light may be reflected. The reflected S-polarized light may be reflected from a mirror 2 provided at the upper side of the beam splitter 1 and then pass through a half-wavelength retarder 4. The reflected S-polarized light may be converted into P-polarized light and then travel to the screen. The P-polarized light transmitted through the beam splitter 1 may pass through a prism 3 provided at the lower side of the beam splitter 1 and travel to the screen.
Although not shown in FIG. 5, as described above, light transmitted through the beam splitter may be modulated by the modulator shown in FIG. 2 and then projected onto the screen.
However, in order to apply such technology to the stereoscopic image device, the following conditions are necessary.
The image of the light emitted from the projector has a predetermined size. In order to implement a stereoscopic image having excellent efficiency and high image quality on the screen, the size of the image displayed on the screen by light traveling along a transmission path and the size of the image displayed on the screen by light traveling along a reflection path should be equal or similar to each other such that the two images overlap each other. That is, in the stereoscopic image device using the beam splitter in order to implement a high-luminance stereoscopic image, as an overlap ratio of lights passing through the two paths on the screen increases, the quality of the stereoscopic image may increase. There is a need for a means for compensating for a path difference between the path of the transmitted light and the path of the reflected light.
In addition, since the mirror 2 of the beam splitter is formed on the prism, manufacturing costs increase. In addition, when light is reflected from the mirror, light loss may occur.